CN1498199A - Method and apparatus for heterogeneous synthesis of compounds - Google Patents

Abstract

A process for the heterogeneous synthesis of chemical compounds such as methanol and ammonia through catalytic conversion of the respective gaseous reactants that are made to pass through a first (2) and a second (3) reaction zone connected in series with each other, in which they react in pseudoisothermal conditions, distinguishes itself in that in the first reaction zone (2) the gaseous reactants are made to flow through a fixed mass of an appropriate catalyst in which a plurality of substantially box-like, plate-shaped heat exchangers (21), arranged side-by-side and crossed by a heat exchange operating fluid, is dipped.

Description

Method and apparatus for heterogeneous synthesis of compounds

Application field

In its broader aspects, the invention relates to a process for the heterogeneous synthesis of compounds such as methanol and ammonia.

In particular, the invention relates to a process of this type comprising two reaction zones connected in series to each other in order to carry out a catalytic chemical reaction under so-called pseudo-isothermal conditions, wherein the reaction temperature is controlled to a value around a predetermined optimum value within a limited range of values.

The invention also relates to a device for carrying out the aforementioned method.

current technology

In the field of industrial production of compounds such as methanol and ammonia, it is well known that there is a need to develop heterogeneous synthesis processes with high conversions of reactants and equipment with large capacities at low investment and energy costs.

In order to meet the above needs, a method for methanol synthesis has been proposed in the art, which comprises two reaction zones connected in series to each other, and operates under pseudo-isothermal conditions, i.e., removal of reaction heat, in which by reacting with the The fresh, recycled reactant stream in the first reaction zone is indirectly heat exchanged to remove excess heat formed in the second reaction zone.

EP-A-0 790 226 describes this method. However, for proper operation and to achieve the desired economic benefits, the first reaction zone must consist of tube bundle exchangers, and the corresponding tubes filled with a suitable catalyst. The gaseous reactants _H2 and CO are passed inside the tubes, while the outside of the tubes are flushed with a flow of water as a heat exchange working fluid (with the generation of steam). A reactor of this type is, for example, the reactor described in US-A-4 559 207 .

GB-A-2 203 427 also confirms the need to use this particular type of reactor in the first reaction zone of the two-step process for the synthesis of methanol.

Although advantageous in all respects, the above-mentioned processes have corresponding and recognized technical drawbacks, which at an industrial level impose certain limitations on the progress or degree of completion (conversion) of the chemical reactions considered and on the production capacity of the individual plants .

In fact, the tube-bundle reactor just described implies a structural and application complexity which only allows the processing of relatively small reaction volumes, as described in EP-A-0 790 226, resulting in impairing the conversions obtainable with this type of reactor. efficiency and productivity disadvantages.

Tube-bundle reactors with relatively large reaction volumes, besides being very difficult to use if possible, require such high investment costs that the two-stage reaction process is no longer cost-effective.

In order to overcome this disadvantage, GB-A-2 203 427 proposes the use of highly efficient catalysts, which however, besides only partially solving the problems of low conversion and productivity in tube bundle reactors, are very expensive.

As a result, due to the aforementioned disadvantages, the processes according to the prior art cannot achieve high conversions and high production capacities in a relatively cost-effective, technically simple and reliable manner.

Summary of the invention

The technical problem of the present invention is to provide a process for the heterogeneous synthesis of compounds such as methanol and ammonia, which is easy to develop and achieves high conversions in chemical plants with large capacities at low investment and energy costs, The disadvantages of the prior art are overcome.

According to the present invention, the above-mentioned technical problems are solved by a process for the heterogeneous synthesis of compounds such as methanol and ammonia by catalytic conversion of individual gaseous reactants passing through first and second reaction zones connected to each other in series, in wherein they react under pseudo-isothermal conditions, the process is characterized by the fact that, in said first reaction zone, the gaseous reactants are passed over a fixed amount of a suitable catalyst, in which many are arranged side by side, and are worked by heat exchange The fluid passes through basically a box-type, plate-shaped heat exchanger.

Advantageously, contrary to the conventional teachings of the prior art, it has surprisingly been found that, thanks to the aforementioned features, in a process of the above-mentioned type, the conversion and the production capacity.

In this case, the aforementioned compounds can be produced in large quantities and at high conversion rates in large-capacity chemical equipment, which is simple in technology development and does not imply high energy consumption and high investment and maintenance costs.

The invention also relates to a chemical device having structural and functional features suitable for carrying out the aforementioned method.

The characteristics and advantages of the method according to the invention will become clearer from the description of indicative and non-limiting embodiments of the invention, with reference to the accompanying drawings.

Brief description of the drawings

Figure 1 shows a block diagram, in a conventional and schematic manner, illustrating an apparatus for carrying out a method according to an embodiment of the invention.

FIG. 2 diagrammatically represents a detailed longitudinal section of the apparatus represented by the block diagram of FIG. 1 .

Detailed description of the drawings

In FIG. 1 , all the main elements of a plant for the production of methanol or ammonia according to the invention are schematically illustrated, the whole of which is indicated by the number 1 .

The apparatus 1 comprises a first reaction zone 2 and a second reaction zone 3 connected in series to each other.

Inside the reaction zones 2 and 3, in a manner known per se, a reaction zone 4 is provided for housing a fixed quantity of a suitable catalyst, not shown.

Reaction zones 2 and 3, when functional, operate under pseudo-isothermal conditions and are therefore fitted with heat exchange units 5 and 6 respectively, in reaction zone 4 interposed in said catalyst.

The reaction temperature in zone 4 of the first reaction zone 2 is controlled by indirect heat exchange by flowing a heat exchange fluid in the unit 5, as indicated by the arrows. In the case of exothermic reactions such as methanol or ammonia synthesis, the heat exchange fluid is, for example, water. During this passage, the water is converted to steam, or simply preheated for subsequent generation of steam in a dedicated boiler placed outside the reaction zone, (not shown).

The reaction temperature in zone 4 of the second reaction zone 3 is controlled by indirect heat exchange by causing a gaseous reactant stream, for feeding to the first reaction zone 2, as heat exchange fluid in the heat exchange unit 6 flow to achieve. In this respect, the duct 7 , which is in fluid communication with the heat exchange unit 6 , enters at this unit 6 into the second reaction zone 3 and exits therefrom into the reaction zone 4 of the first reaction zone 2 .

Line 7, as well as unit 6, are traversed by gaseous reactant streams such as _H2 and CO for methanol synthesis, _H2 and _N2 for ammonia synthesis, all fresh and recycled.

Also, the conduit indicated by numeral 8 connects the outlet of zone 4 of the first reaction zone 2 in fluid communication with the inlet of zone 4 of the second reaction zone to feed the reaction mixture thereto, said reaction mixture comprising methanol or ammonia and Unreacted gaseous reactants obtained in reaction zone 2.

Coming out of zone 4 of the second reaction zone 3, a duct 9 is finally arranged to discharge the final reaction mixture, which besides methanol or ammonia also contains a portion of unreacted gaseous reactants.

In the region of the apparatus of FIG. 1 which is in fluid communication with line 9 and is not shown, the methanol and ammonia thus obtained are separated from the reaction mixture, and the gaseous reactants present in this mixture are passed through line 7 with freshly fed gaseous reactants Recycle to first reaction zone 2.

According to a feature of the present invention, in addition to being inserted into the catalyst in the reaction zone 4, the heat exchange unit 5 is composed of a plurality of substantially box-type, plate-shaped heat exchangers arranged side by side and traversed by a heat-exchanging working fluid, as shown in Fig. 2, Figure 2 shows the first reaction zone 2 in more detail.

In this figure, the first reaction zone 2 consists of a pseudo-isothermal reactor comprising a cylindrical shell 10 closed at opposite ends by respective upper and lower bases 11, 12, and containing mounted plate-shaped elements The heat exchange unit 5 will be exemplified in the following description.

The upper base 12 is equipped with nozzles 13, so that the gaseous reactants from the pipeline 7 in FIG. out.

The lower base 11 is fitted with nozzles 16 to bring the effluent of the reaction mixture from the reactor 2 into fluid communication with the conduit 8 of FIG. 1 .

Inside the housing 10 is installed a reaction zone 4 containing an annular catalytic bed 17 known per se, open upwards and whose side walls are perforated for the radial or axial-radial passage of the gaseous reactants through the catalytic bed.

The inner wall of the catalytic bed 17 forms a channel 18 inside it, the upper part is closed by a cover 19, and is in fluid communication with the nozzle 16 through a joint 20 to discharge the reaction mixture.

In the reaction zone 4 , and more precisely inside the catalytic bed 17 , a heat exchange unit 5 is installed in a manner conventional in nature, interspersed with a mass of suitable catalysts, not represented.

According to this embodiment, the heat exchange unit 5 has a substantially cylindrical shape and comprises a plurality of flat, substantially box-like, plate-shaped heat exchangers 21 having a parallelepiped shape arranged side by side in a coaxial And concentric elements (basically arranged radially).

More specifically, although not shown, each heat exchanger 21 is preferably composed of a pair of side-by-side metal plates interconnected by circumferential welding in a predetermined distance relationship such that a compartment 21a (indicated by dashed lines) is interposed between them, intended to To be traversed by the heat exchange working fluid.

For the working fluid mentioned above, on the relatively long side 22 of each heat exchanger 21 , each heat exchanger 21 is respectively installed with a distribution pipe 23 and a collection pipe 24 . For said working fluid, tubes 23 and 24 are in fluid communication with said compartment 21a on one side through at least one, but preferably through a plurality of openings or holes (not shown), wherein, along one or more matrixes, and at Opposite, on the outside of the exchanger 21 , they are mounted via respective inlet and outlet pipe connections 25 and 26 . Connectors 25 and 26 are in turn connected to nozzles 14 and 15, respectively.

In order to facilitate the passage of the heat-exchanged working fluid by the heat exchanger 6 in a radial or substantially radial direction, the compartment 21a is preferably divided into a plurality of parts, not directly communicating with each other, and for example by means of a corresponding number of welds or Separate baffles (indicated by dotted lines) are obtained, said welds or baffles extending vertically to the distributor 23 and header 24 of the exchanger 21 .

Thanks to this embodiment of the first reaction zone 2, it is possible to carry out the process according to the invention, wherein a gaseous reactant is passed through a fixed amount of a suitable catalyst of this reaction zone, wherein a plurality of them are arranged side by side and are heat exchanged A basically box-type, plate-shaped heat exchanger through which the working fluid passes.

In this case, it may be advantageous to develop a first reaction zone 2 with low energy expenditure even in the case of large-space (volume) reactions in a simple, reliable and economical manner.

In other words, the presence of plate-shaped heat exchangers inserted into the catalytic mass, in addition to being particularly efficient as indirect heat exchange elements, allows an arbitrary dimensioning of the first reaction zone 2 and thus a high conversion rate in this reaction zone And high production capacity, which is beneficial to the overall conversion rate and the development of equipment with large capacity.

It is therefore contemplated that variations and modifications may be made to the invention, all within the scope of protection defined in the appended claims.

For example, according to a preferred embodiment of the present invention, the reaction mixture coming from the first reaction zone 2 and fed to the second reaction zone 3 via line 8 may advantageously be cooled by means of indirect heat exchange in a heat exchanger 27 of conventional type , the heat exchanger 27 is represented by a dotted line in FIG. 1 . In this way, not only is it possible to recover heat for the production of steam for use eg in other parts of the steam plant, but above all it is possible to control the inlet temperature of the second reaction zone 3 and thus its conversion.

Alternatively, it is also possible to foresee that part of the “fresh” gaseous reactants and/or part of the recycled reactants are fed directly to the first reaction zone 2 via the conduit 28 without passing through the second reaction zone 3 .

The heat exchange unit 6 can be of conventional type, ie in the form of a tube bundle or coil, or advantageously it can also consist of a plurality of plate heat exchangers as described with reference to FIG. 2 . In this case, it is possible to obtain a further increase in the conversion rate and growth capacity of the chemical plant.

According to another embodiment of the present invention, not depicted, the first and second reaction zones 2, 3 may be enclosed in a single synthesis reactor instead of having two reactors as in the example of FIG. 1 .

The temperature of the operating conditions within the reaction zone is conventional for methanol or ammonia synthesis. As long as it is taken into account that the pressure operating conditions are in particular to the results already obtained by operating the two reaction zones 2 and 3 at substantially the same pressure, and preferably 50-100 bar for methanol synthesis and 50-300 bar for ammonia synthesis , preferably 80-150 bar.

Claims (6)

1. Process for the heterogeneous synthesis of methanol or ammonia by catalytic conversion of respective gaseous reactants passing through first (2) and second (3) reaction zones connected in series to each other, in which said The reaction of gaseous reactants under pseudo-isothermal conditions is characterized in that, in said first reaction zone (2), the gaseous reactants are made to flow through a fixed amount of a suitable catalyst, in which a plurality of side-by-side A substantially box-like, plate-shaped heat exchanger (21) is arranged and traversed by a heat-exchanging working fluid. 2. A method according to claim 1, characterized in that the pressure inside said reaction zones (2, 3) is substantially the same. 3. The method according to claim 1, characterized in that said gaseous reactants are fed into said first reaction zone (2) after indirect heat exchange with the reaction mixture inside said second reaction zone (3), said The reaction mixture is fed to the subsequent reaction zone (3) and from said first reaction zone (2). 4. The method according to claim 1, characterized in that the reaction mixture from the first reaction zone (2) is fed into the second reaction zone (3), and the second reaction zone (3) Indirect heat exchange is performed in advance in order to control the inlet temperature of the second reaction zone (3). 5. Process according to claim 1, characterized in that a mixture of gaseous reactants comprising "fresh" gaseous reactants and recycled gaseous reactants is fed into said first reaction zone (2), said recycled Gaseous reactants are suitably separated from the reaction mixture from said second reaction zone (3). 6. A device for heterogeneous synthesis of methanol or ammonia by catalytic conversion of gaseous reactants, comprising first (2) and second (3) reaction zones connected in series to each other, arranged in said first and second reaction zones ( 2, 3) in the respective heat exchange units (5, 6), characterized in that in the first reaction zone (2), the heat exchange unit (5) is inserted into the catalytic substance, and comprises a plurality of A substantially box-type, plate-shaped heat exchanger (21) to be traversed by a heat-exchanging working fluid.

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